Edexcel Jun 2012 Paper 2 Q19 (with explained solutions) |

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Edexcel Jun 2012 Paper 2 Q19

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19 Metal nitrates decompose on heating. Potassium nitrate, KNO3, decomposes to form potassium nitrite and oxygen, whereas calcium nitrate, Ca(NO3)2, decomposes to form calcium oxide, nitrogen dioxide and oxygen. (a) Write equations for the decomposition of each of these metal nitrates. State symbols are not required. (i) Potassium nitrate (ii) Calcium nitrate (b) State two things that you would see when anhydrous calcium nitrate is heated. (2) (2)*(c) Explain why potassium nitrate and calcium nitrate decompose to form different products. (3)(Total for Question 19 = 7 marks) TOTAL FOR SECTION B = 40 MARKS *P39307A01520* 15 Turn over<br />

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Reject Mark Reject Mark Reject Mark Acceptable Answers 2KNO32KNO2 + O2 Or multiples or equation divided by 2 ALLOW O2 on LHS if balanced by additional O2 on RHS IGNORE state symbols even if incorrect Acceptable Answers 2Ca(NO3)22CaO + 4NO2 + O2 Or multiples or equation divided by 2 ALLOW O2 on LHS if balanced by additional O2 on RHS IGNORE state symbols even if incorrect Acceptable Answers Brown gas (ALLOW fumes or vapour) evolved (1) IGNORE Effervescence/bubbles EITHER (White) solid melts (and then solidifies/freezes) OR (Colourless) liquid forms (1) IGNORE white solid formed Question Number 19 (a)(i) Question Number 19 (a)(ii) Question Number 19 (b)<br />
Reject Mark Acceptable Answers Penalise any omission of reference to ion in MP 1 only but calcium ions or Ca2+ and potassium ions or K+ are equivalent Marking Point 1 Calcium ions have greater positive charge (than potassium ions) OR Calcium ions 2+ but potassium ions 1+ OR Ca2+ but K+ OR calcium ions are smaller (than potassium ions) OR calcium ions have greater charge density (1) Marking Point 2Calcium (ions) more polarising or cause greater distortion (1) Marking Point 3 Of nitrate (ion) OR anion OR NO / N=O(bond) OR nitrate electron cloud (1) Reverse argument for K+ gains full marks TOTAL FOR SECTION B = 40 MARKS Question Number 19 (c)<br />

Question 17 18 19 20

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